A self-closing valve is standard for use on flush toilets and urinals and in institutional or commercial settings on a faucet. Such a valve opens when actuated and then closes a predetermined time after opening, so that water is not wasted.
As described in U.S. Pat. No. 4,899,778 of Laube an autoclosing flow-control valve has a housing forming an inlet chamber normally filled with a fluid under pressure, an outlet chamber, and a valve seat between the chambers. A piston defines in the chamber a control chamber and carries a valve element engageable with the seat. The piston and valve element are displaceable in the housing between a closed position with the element engaging the seat and blocking flow between the chambers and an open position with the element clear of the seat and permitting flow from the inlet chamber to the outlet chamber. A spring braced between the piston and the housing urges the piston and element backward into the closed position. The control chamber is of substantially smaller volume in the closed position than in the open position and the piston is formed with a small bleed passage extending between the control chamber and the outlet chamber. A control passage extending between the inlet chamber and the control chamber is provided with a pilot valve for, in an open position of the pilot valve, pressurizing the control chamber and pushing the piston and element into the open position and, in a closed position of the pilot valve, for blocking flow through the control passage. A control element, hereinafter termed a knob is movable on the housing to open the pilot valve.
Thus with this arrangement the knob is actuated to open the pilot valve so the pressurized water floods the control chamber and opens the valve. As soon as the knob is released the pilot valve closes and the piston and valve element are moved slowly back into the closed position by the spring as the pressure in the control chamber bleeds out through the small bleed passage. The open time is controlled by how much liquid is admitted to the control chamber.
Such a valve assembly has several drawbacks. First of all it offers the user minimal control over the amount of liquid dispensed. While the open time can be extended by holding down the knob, thereby holding the pilot valve open, this open time cannot be shortened. No matter what, the user must wait until the valve closes.
Furthermore adjusting the open time of such a valve is a fairly tricky job. It entails the painstaking disassembly of the valve to move abutments or change the bleed-passage size. Such an adjustment cannot be carried out without disassembly of the device.
Finally the known systems cannot in generally be serviced at all without turning off the water. The valve must be depressurized completely before any of its parts can be accessed.